unusual lines on tail fin in Disease Diagnosis/ Treatments Posted October 19, 2018 hey everyone, my fish has been acting strange as of late. for a while he was just acting quiet and stressed out so i just decided to leave him alone in fear of adding to the stress. he wasn’t eating for a couple of days so i reduced the amount i was feeding him. he started acting a bit more social so i started to feed him his usual amount. i noticed that he was struggling to swim and he wasn’t moving his tail fin often so i investigated. i found the strange white/pinkish lines across his tail. i couldn’t seem to find anything like this while searching online. i apologise if i gave an unnecessary amount of information, but i wanted to give the full story. it’s also worth mentioning that his tank mate died of strange, unknown causes before he became timid and stressed. when the other fish died his. usually black and gold body was white and pink. the now dead fish made a habit of eating pebbles and i’m not sure if that was related to his death.